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Discussion Starter · #1 ·
My transmission started slipping between 1st and second gear on my 04 Avalanche. I replaced the transmission. Then the transfer case started grinding when I let off the gas above 30 mph. It also grinds in reverse when in 2 WD and 4 Hi, but no noise when in reverse while in 4 Lo. I went ahead and replaced the bearings, seals, upgraded pump and range fork. It still does the same thing. My truck has 171,000 miles on it. I did try a used transfer case that drove good but the pump chattered way to much and the housing has hole started. Please help! Thank you.
 

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My transmission started slipping between 1st and second gear on my 04 Avalanche. I replaced the transmission. Then the transfer case started grinding when I let off the gas above 30 mph. It also grinds in reverse when in 2 WD and 4 Hi, but no noise when in reverse while in 4 Lo. I went ahead and replaced the bearings, seals, upgraded pump and range fork. It still does the same thing. My truck has 171,000 miles on it. I did try a used transfer case that drove good but the pump chattered way to much and the housing has hole started. Please help! Thank you.
04, I'm guessing full auto shift, still have the motor and senders off the other tcase, or did they get swapped when you swapped units?
 

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I still have them but I did swap out encoder motor and sensors to make sure.
OK, that's where I was going with that...out of curiosity... Did you see how everything shifted, w motor out? By hand I mean...seeing if things fully engaged?
Edit, see you did range fork... So you probably did....
 

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Maybe pump, pickup, ended up in a weird spot?
 

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I guess clutches could...I'll, look at an explosion see what I can find, chain tension? In neutral, is there a lot of play in drive lines?
 

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Discussion Starter · #10 ·
I guess clutches could...I'll, look at an explosion see what I can find, chain tension? In neutral, is there a lot of play in drive lines?
The chain tension seems to be ok. I’m not really sure how tight it should be. There’s some play in the drive line but not a lot. After looking at it for a little bit. Doesn’t the clutches and chain only control the front shaft? It seems like it’s not going in gear completely in 2 Wd causing it to slip when there is no tension on it. But 4 lo is fine.
 

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That's kind of what I keep coming back to in my head, is engagement, but I don't have it in my hands (sometimes this side of the net can be rough:confused:) usually if chain is slack, you can tell by drive line movement, its kind of difficult to tell by looking (at least for me) unless its obvious. Do you still have it apart? No excessive ware on the blocking rings or shift collar? How about the fork...are the nubs on there? Does this one have plastic shims on the fork nubs where the collar rides or just metal?
 

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What is your case number? Np---or ---- ?
 

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Discussion Starter · #14 ·
It’s NP 246. It has the plastic nubs on the range fork they are New I replaced them. I don’t see any play or wear on the selector plate. I did also put new clamp rings.
Ok today I went through the whole tcase again. Everything is working like it should. It still does the same thing. I went ahead and got a used one with 80,000 miles. I put it in and the same problem. What else could cause this besides the case itself?
 

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I thought the other case you used didn't do this?.... Must have misunderstood, bad CV axles up front, bad u joints, a/b solenoid issue...Ie. Solenoids actuating at wrong time, or together....had a guy attempt a 60 to 80 e swap, but didn't understand the a/b solenoids are run in reverse of each other...ground in gears at certain points.
 

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Discussion Starter · #16 ·
I thought the other case you used didn't do this?.... Must have misunderstood, bad CV axles up front, bad u joints, a/b solenoid issue...Ie. Solenoids actuating at wrong time, or together....had a guy attempt a 60 to 80 e swap, but didn't understand the a/b solenoids are run in reverse of each other...ground in gears at certain points.
No you didn’t misunderstand. I did try one case that didn’t do this but the pump was clicking really loud and a hole was almost through it. Since then I have tried 2 more that did this and the one I rebuilt does this. The CV axles are good and U-joints are good. My transmission was a 60 and I replaced it with a 60 supposedly out of an Avalanche. I don’t know about the solenoids I will do some checking. Any advice on where to start? Thank you very much for all your replies and patience!
 

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Discussion Starter · #17 ·
Some other info that may be helpful. I’ve been sitting here thinking about the whole process that I’ve been doing. The transmission went out the first week of December and working on it since then. When I first started taking it out I forgot to disconnect the battery cable and the plug for the truck side of the encoder motor arced and sparks flew. I found the fuse for the radio had blown and I replaced it and checked the others that was the only one I found blown. I had completely forgotten about that.
 

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Well, I guess that's a place to start, make sure everything encoder wise is good...check for burnt pins...the a/b shift for all 60es is the same (from what I know anyway) but it may still be a good thing to check on. (Although, if you had a case, that did not do this...its a scratcher :confused:) maybe the case that doesn't do this, doesn't operate appropriately in some way? Or maybe... Its right, and the other two, share the same issue...If I remember right, we swapped encoders, and sensors already.. And tried manual shifting...all netting the same results. So...what if you completely disable the unit...put encoder in manually... And pull all fuses related?
 

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Discussion Starter · #19 ·
Could the transmission still be bad? When I put the transfer switch in neutral the Avalanche will not go into drive or reverse. I remember before the transmission went out it would still go into drive and reverse even with the transfer in neutral.
 
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